%{c,JSESSIONID} is not enough, since according to the Java Servlet Specification 3.1 Final:

7.1.3 URL Rewriting
URL rewriting is the lowest common denominator of session tracking. When a client
will not accept a cookie, URL rewriting may be used by the server as the basis for
session tracking. URL rewriting involves adding data, a session ID, to the URL path
that is interpreted by the container to associate the request with a session.
The session ID must be encoded as a path parameter in the URL string. The name of
the parameter must be jsessionid. Here is an example of a URL containing encoded
path information:
http://www.myserver.com/catalog/index.html;jsessionid=1234

I'm unaware whether the actual feature is supported yet. I hope it is, because I may need it for porting some legacy JSP pages.